Three-dimensional waveguide sensors for sample analysis

ABSTRACT

Systems and methods for measuring a characteristic of a fluid are provided. The system includes a plurality of waveguides embedded in a substrate, and an exposed surface of the substrate comprising a portion of a side surface of at least one of the plurality of waveguides. The system also includes a sensitized coating in the at least one of the plurality of waveguides. The exposed surface is curved in a direction perpendicular to a light propagation in the waveguide. A method of fabricating a system as above is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority under 35 U.S.C. §120 as a divisional from U.S. patent application Ser. No. 14/781,053,entitled “THREE-DIMENSIONAL WAVEGUIDE SENSORS FOR SAMPLE ANALYSIS,”filed on Sep. 29, 2015, which is the national stage entry ofInternational Application No. PCT/US2014/058818, entitled“THREE-DIMENSIONAL WAVEGUIDE SENSORS FOR SAMPLE ANALYSIS,” filed on Oct.2, 2014, the disclosures of which are hereby incorporated by referencein their entirety for all purposes.

BACKGROUND

The present disclosure relates to sensors incorporating waveguides in athree-dimensional (3D) substrate for use in the oil and gas industry.More specifically, the present disclosure relates tointerferometry-based chemical sensors to measure fluid samples relevantin the oil and gas industry.

Chemical sensors using planar waveguide arrays in a Mach-Zehnderinterferometer configuration have gained popularity for their highsensitivity. However, planar geometries are incompatible with therelatively large and circular cross-sections of optical fibers used toreach the depths of some wellbores in oil and gas exploration andextraction operations. In such downhole environments, the fragilecomplexion of planar waveguide arrays becomes a hindrance, as alignmentprocedures need to be enhanced. Also, planar waveguide arrays are moresusceptible to stress, strain, high temperatures, and high pressurescommonly encountered in downhole applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of thepresent disclosure, and should not be viewed as exclusive embodiments.The subject matter disclosed is capable of considerable modifications,alterations, combinations, and equivalents in form and function, withoutdeparting from the scope of this disclosure.

FIG. 1 illustrates a measurement system including a sensor incorporatingwaveguides in a 3D substrate, according to some embodiments.

FIG. 2A illustrates a cross-sectional view of a sensor incorporatingwaveguides in a 3D substrate, according to some embodiments.

FIG. 2B illustrates a cross-sectional view of a sensor incorporatingwaveguides in a 3D substrate, according to some embodiments.

FIG. 3A illustrates a cross-sectional view of a sensor incorporatingwaveguides in a 3D substrate, according to some embodiments.

FIG. 3B illustrates a cross-sectional view of a sensor incorporatingwaveguides in a 3D substrate, according to some embodiments.

FIG. 4 illustrates a chemical sensor incorporating waveguides in anexterior surface of a 3D substrate, according to some embodiments.

FIG. 5 illustrates a chemical sensor incorporating waveguides in aninterior surface of a 3D substrate, according to some embodiments.

FIG. 6A illustrates a cross-sectional view of a sensor incorporatingwaveguides in an exterior surface of a 3D substrate, according to someembodiments.

FIG. 6B illustrates a cross-sectional view of a sensor incorporatingwaveguides in an interior surface of a 3D substrate, according to someembodiments.

FIG. 6C illustrates a side view of the sensors of FIGS. 6A and 6B,according to some embodiments.

FIG. 7 illustrates a flow chart including steps in a method forfabricating a sensor incorporating waveguides in a 3D substrate,according to some embodiments.

FIG. 8 illustrates a flow chart including steps in a method formeasuring a characteristic of a sample using a sensor, according to someembodiments.

FIG. 9 illustrates an exemplary drilling system employing a sensorincorporating waveguides in a 3D substrate, according to someembodiments.

FIG. 10 illustrates a well system employing a sensor incorporatingwaveguides in a 3D substrate, according to some embodiments.

DETAILED DESCRIPTION

The present disclosure relates to sensors incorporating waveguides in athree-dimensional (3D) substrate for use in the oil and gas industry.More specifically, the present disclosure relates tointerferometry-based sensors to measure fluid samples relevant in theoils and gas industry.

Measurement of fluid samples, as disclosed herein, includes measuring acharacteristic or analyte of relevance in the sample. Embodiments asdisclosed herein make use of the optical interaction between a samplewith a first portion of an electromagnetic radiation. An associatedsensor combines an interacted first portion of the electromagneticradiation with a second portion of the electromagnetic radiation toproduce a signal in a photo-detector. An analyzer determines changes inthe signal and correlates the changes with a presence, absence, or achange in the characteristic in the sample. In that regard, theembodiments disclosed herein interferometrically combine the interactedfirst portion and the second portion of the electromagnetic radiation(e.g., as in a Mach-Zehnder type interferometer). Sensors of a typeconsistent with the present disclosure may include chemical sensors, pHsensors, biological sensors, and other environmentally sensitive devicessuch as physical sensors correlating an optical signal to a fluiddensity.

As used herein, the term “characteristic” refers to a chemical,mechanical, or physical property of a substance. The characteristic of asubstance may include a quantitative or qualitative value of one or morechemical constituents or compounds present therein or any physicalproperty associated therewith. Such chemical constituents and compoundsmay be referred to herein as “analytes.” Illustrative characteristics ofa substance that can be detected with the sensors described herein caninclude, for example, chemical composition (e.g., identity andconcentration in total or of individual components), phase presence(e.g., gas, oil, water, etc.), impurity content, pH, alkalinity,viscosity, density, ionic strength, total dissolved solids, salt content(e.g., salinity), porosity, opacity, bacteria content, total hardness,transmittance, combinations thereof, state of matter (solid, liquid,gas, emulsion, mixtures, etc.), and the like.

As used herein, the term “substance,” “sample,” “sample substance,” orvariations thereof, refers to at least a portion of matter or materialof interest to be tested or otherwise evaluated using embodimentsdescribed herein. The substance includes the characteristic of interest,as defined above. The substance may be any fluid capable of flowing,including particulate solids, liquids, gases (e.g., air, nitrogen,carbon dioxide, argon, helium, methane, ethane, butane, and otherhydrocarbon gases, hydrogen sulfide, and combinations thereof),slurries, emulsions, powders, muds, glasses, mixtures, combinationsthereof, and may include, but is not limited to, aqueous fluids (e.g.,water, brines, etc.), non-aqueous fluids (e.g., organic compounds,hydrocarbons, oil, a refined component of oil, petrochemical products,and the like), acids, surfactants, biocides, bleaches, corrosioninhibitors, foamers and foaming agents, de-foamers, breakers,scavengers, stabilizers, clarifiers, detergents, a treatment fluid,fracturing fluid, a formation fluid, or any oilfield fluid, chemical, orsubstance as found in the oil and gas industry.

As used herein, the term “electromagnetic radiation” includes radiowaves, microwave radiation, terahertz, near/mid/deep infrared radiation,visible light, ultraviolet light, X-ray radiation and gamma rayradiation.

As used herein, the term “optically interact” or variations thereofrefers to the reflection, transmission, scattering, diffraction,interference, or absorption of electromagnetic radiation either on,through, or from one or more processing elements, a substance beinganalyzed by the processing elements, or a polarizer. Accordingly,optically interacted light refers to electromagnetic radiation that hasbeen reflected, transmitted, scattered, diffracted, interfered, orabsorbed by, emitted, or re-radiated, for example, using a sensitizedcoating, but may also apply to optical interaction with a substance or apolarizer. In operation, a sensor as described herein is capable ofdistinguishing electromagnetic radiation related to a characteristic ofinterest of a substance from electromagnetic radiation related to othercomponents of the substance.

Embodiments disclosed herein include sensors for measuring acharacteristic of a sample substance by interacting electromagneticradiation with the sample substance. Sensors based on interferometryshow high sensitivity. An interferometer, in embodiments consistent withthe present disclosure, splits coherent electromagnetic radiation intoat least two portions that effectively travel different optical pathsbefore being recombined and detected. An optical path length is definedas the product of the refractive index of the material the radiation orlight is propagating through and the physical propagation distance orlength. For waveguides, the effective refractive index used in thecalculation of optical path length is based on the propagation velocityof waves in the waveguide. The difference in the optical path lengthsbetween a first portion and a second portion of the electromagneticradiation creates a change in interference fringe pattern uponrecombination. The fringe pattern carries information regarding a sampleproperty of interest (e.g., substance or analyte concentration amongmany others). The fringe pattern provides a sensitive measure of thephase shift induced by propagation of radiation under the presence (orabsence) of an analyte of interest. Accordingly, interferometrictechniques as disclosed herein allow for enhanced sensitivity at verylow concentrations of the analyte of interest.

Embodiments as disclosed herein use interferometry with chemicallysensitized optical waveguides to enhance detection sensitivity whilemaintaining device simplicity and compactness. In extreme environmentalconditions, a waveguide structure embedded in a 3D substrate is wellsuited for interferometry. The oil and gas industry may benefit fromsuch embodiments by using already deployed fiber optic cables andinfrastructure in oil wells and pipelines. Embodiments as disclosedherein may be used in the inspection and maintenance of oil and gaspipelines used for long-haul transportation, or within refineries andstorage facilities.

Embodiments in this disclosure combine existing technologies used in themanufacturing of optical fibers to form waveguides on interior andexterior surfaces of a 3D substrate. Pairs of waveguides are formed intoMach-Zehnder interferometers. A coating to selectively absorb, capture,bind, or otherwise immobilize a target analyte (i.e., characteristic) isapplied to one arm of the Mach-Zehnder interferometer while thereference arm remains uncoated. In some embodiments, coherent lightilluminates one end of the 3D substrate and launches light into bothsensing and reference arms. Since one arm is coated and one is not, thequantity of the target analyte absorbed, captured, bound, or immobilizedwill cause a change in phase difference at the output of the two arms.Light leaving the two arms will spread out or diffract as it propagatesthrough free space, overlapping and forming an interference pattern onan optical detector. The interference pattern observed at the detector,or a received irradiance of a single detection point is a function ofthe analyte absorbed, captured, bound, or immobilized in the coated arm.

Sensors as disclosed herein incorporate a plurality of waveguides into a3D structure arranged in various configurations to detect one or moreproperties of a downhole environment. Sensitivity and specificity ofsensors as disclosed herein are enhanced by coating alternatingwaveguide channels with a sensitized coating layer or film. Thesensitized coating can be located on an outer surface or an innersurface of the 3D structure, depending on the configuration of thesensor. In either configuration, the sensitized coating is located on asurface exposed to the sample. Some embodiments include one or moredifferent sensitized coatings to interact with one or more analytes ofinterest in the sample. In this sense, combinations for analytedetection are unlimited, as functional coatings are identified fordifferent target analytes of interest. The interaction of an analytewith a sensitized coating causes a change in the refractive index of thecoating. The change in the coating refractive index changes thepropagation constant of the coated waveguide. Some embodiments use theinteraction of an evanescent field from a propagating waveguide modewith the sensitized waveguide surface to change an interference patternbetween the light emanating from the sensitized waveguide and lightemanated from a reference waveguide. This change is generallyproportional to analyte concentration.

A sensitized coating is activated when it absorbs, binds, attaches, oradheres to a target analyte(s) such that the refractive index of thesensitized coating changes. This changes the propagation constant of thesample waveguide, thereby giving rise to a phase shift of light (i.e.,electromagnetic radiation) emerging from the sample waveguide. If aninterferometer is constructed containing the sample waveguide and anuncoated reference waveguide, the output of the interferometer changesin response to activation of the sample waveguide by the presence of thetarget analyte. An analyzer determines a target analyte concentrationbased on the change in the interference pattern. Embodiments disclosedherein include arrangements of sample and reference waveguides to makean interferometry configuration simple to adapt for field applicationsand for simultaneous measurement of multiple target analytes.

In some embodiments, the plurality of waveguides forms an array having acircular cross-section relative to the light propagation in thewaveguides. This configuration makes the sensor suitable for downholeand pipeline applications in the oil and gas industry. Embodimentsconsistent with this disclosure include small and robust chemicalsensors that use relatively low power and are relatively inexpensive tofabricate. Furthermore, sensors according to this disclosure have theability to measure a plurality of sample characteristics of interestsimultaneously with no moving parts.

FIG. 1 illustrates an exemplary measurement system 101 including asensor 100 incorporating waveguides 114 in a 3D substrate 105, accordingto some embodiments. In embodiments consistent with the presentdisclosure, sensor 100 may be a chemical sensor configured to detect thepresence and/or concentration of one or more chemical analytes ofinterest in a sample. Sensor 100 includes a light source 102, and a beamsplitter element 104 to separate the electromagnetic radiation emittedfrom the light source 102 into a first electromagnetic radiation 110 sand a second electromagnetic radiation 110 r. Beam splitter element 104may be any type of phase-preserving beam splitter as known to those ofordinary skill in the art. For example, beam splitter element 104 may bea fiber beam splitter or a beam splitter prism. Light source 102 may bea lamp, an LED, a laser, an electromagnetic radiation emitter, or evensolar light. Sensor 100 includes a detector 118 that provides a signalto analyzer 160. The coherence length of the electromagnetic radiationemitted by light source 102 is desirably as long as or longer than themaximum difference in optical path lengths splitter element 104 todetector 118. Analyzer 160 includes a processor circuit 161 and a memorycircuit 162. Analyzer 160 may also be configured to control light source102.

According to some embodiments, at least one of waveguides 114 includes asurface that is exposed to a fluid 150 in a container 170. In someembodiments container 170 is a closed container that houses fluid 150.Some embodiments include an open container 170 having an inlet and anoutlet so that fluid 150 is circulating or otherwise in motion. In someembodiments, fluid 150 may include a mixture of oil, gas, water, and mud(i.e., drilling fluid) commonly found in downhole environmentsassociated with an oil and gas platform in the oil and gas industry. Inother embodiments, however, fluid 150 may include a blood sample, andfluid container 170 may be a vile, a test tube, or a blood vessel in apatient's body. Further according to some embodiments, fluid 150 may bea food product, such as milk or water, and container 170 may be a bottleor package. In some embodiments container 170 may be a pipeline, a tube,or a conduit. For example, container 170 may be an oil or gas pipeline,a water pipeline for agricultural irrigation or drainage, a bloodvessel, or another tissue in the human body. Container 170 may also be aline or fluid passage in a downhole tool or downhole sensor, or a sensorlocated at the surface.

FIG. 2A illustrates a cross-sectional view of an exemplary sensor 200 aincorporating waveguides in a 3D substrate 205 a, according to someembodiments. Chemical sensor 200 a includes sample waveguides 214 s andreference waveguides 214 r embedded in or otherwise positioned onsubstrate 205 a. Waveguides 214 s and 214 r are collectively referred tohereinafter as waveguides 214. Sample waveguides 214 s include asensitized coating 212, 222, 232, and 242. Reference waveguides 214 rare similar in all respects to sample waveguides 214, except forsensitized coatings 212, 222, 232, and 242. It is desirable thatsensitized coatings 212, 222, 232, and 242 provide a linear, reversible,secure, and high target specificity.

In some embodiments, substrate 205 a includes a preform, re-shaped usingtechniques well-known in the optical fiber industry. Accordingly, insome embodiments, 3D substrate 205 a is a glass cylinder. It should benoted that the cross-section of the final 3D substrate 205 a is a scaleddown version of the preform. In embodiments where the preform is a solidrod-like structure, waveguides 214 could be located along the outerdiameter (OD) of the rod. To efficiently propagate electromagneticradiation, waveguides 214 are formed of a material having a higherrefractive index (n₁) than the material in substrate 205 a withrefractive index (n₂, i.e., n₂<n₁).

Sensing channels 210, 220, 230, and 240 are indicated by dashed lines.For each sensing channel 210, 220, 230, and 240, the signal portions ofthe electromagnetic radiation are injected into or otherwise conveyedthrough signal waveguides 214 s, and the reference portions of theelectromagnetic radiation are injected into or otherwise conveyedthrough reference waveguides 214 r. Ideally, the coherent lightilluminating for both reference and sensing waveguides should be inphase. For each sensing channel 210, 220, 230, and 240 an outputelectromagnetic radiation from waveguide 214 s forms an interferencepattern with an output electromagnetic radiation from waveguide 214 r.An interference pattern for each of sensing channels 210, 220, 230, and240 can be measured independently. Thus, sensor 200 a can measure aplurality of analytes either simultaneously or overlapping in time.Waveguides 214 s include sensitized coatings 212, 222, 232, and 242 on aside of the waveguide exposed to the outside or 3D substrate 205 a. Eachof sensitized coatings 212, 222, 232, and 242 may be selected tochemically interact with a target analyte.

FIG. 2B illustrates a cross-sectional view of a chemical sensor 200 bincorporating waveguides 214 in a hollow or cylindrical 3D substrate 205b, according to some embodiments. Sensor 200 b is similar to chemicalsensor 200 a, and operates under the same principles. In that regard,chemical sensor 200 b differs from sensor 200 a in that substrate 205 bis a hollow, 3D structure. Furthermore, in sensor 200 b waveguides 214are disposed along the inner diameter (ID) of substrate 205 b.Accordingly, fluid 150 is contained or flowing through a lumen or cavity207 defined within hollow substrate 205 b.

FIGS. 2A and 2B show the arrangement of waveguides 214 on an exposedsurface of a 3D substrate to form sensing channels 210, 220, 230, and240 as a plurality of interferometers arranged in a 3D configuration.More particularly, a 3D configuration in substrates 205 a and 205 bincludes a cross-section and a length, where the length extends along alongitudinal axis of a wellbore in oil and gas exploration andextraction operations. In some embodiments, the exposed surface is incontact with fluid 150. More generally, the exposed surface is coupledto the substance containing an analyte of interest for measurement. Theexposed surface may be external to an internal diameter of the 3Dsubstrate (e.g., substrate 205 a) or contained within the internaldiameter of the 3D substrate (e.g., substrate 205 b). In embodimentsconsistent with the present disclosure, the exposed surface may includea side surface of each waveguide 214, or at least one of waveguides 214.More generally, the exposed surface may include a side surface of atleast one of waveguides 214, and a portion of the 3D substrate.Advantageously, the cylindrical geometry of sensors 200 a and 200 bmatches the general symmetry of downhole and pipeline inspection toolsin the oil and gas industry. More generally, the exposed surface of the3D substrate may be curved in a direction perpendicular to a lightpropagation in waveguides 214 (i.e., the outer diameter in FIG. 2A andthe inner diameter in FIG. 2B are perpendicular to waveguides 214). Insome embodiments, the outer diameter (OD) of 3D substrates 205 a and 205b is between about 1/16″ and about ⅛″. The cross-sectional dimension ofwaveguides 214 may be on the order of the size of the wavelength oflight propagating through the waveguides. In that regard, waveguides 214may be single mode or multimode waveguides, without limiting theembodiments disclosed herein.

While FIGS. 2A and 2B illustrate waveguides 214 having a somewhat squareprofile, the specific cross-sectional shape and size of waveguides 214is not limiting. Rather, waveguides 214 may have any cross-sectionalshape and size as desired for efficient electromagnetic radiationpropagation and efficient fabrication. In that regard, thecross-sectional shape and size of each pair of waveguides 214 s and 214r within each one of sensing channels 210, 220, 230, and 240 is similaror the same.

Sensitized coatings 212, 222, 232, and 242 may include hydrophobic orhydrophilic gels. Accordingly, either by swelling or shrinking, a changein the refractive index and the geometry of waveguides 214 s induces aphase shift in the sample portion of radiation propagating therethrough.In some embodiments, the sensitized coating 212, 222, 232, and 242 is aporous material that is filled or emptied by the target analyte. Ahydrophilic gel will shrink or swell in the presence of water or oil influid 150. Likewise, a hydrophobic gel may shrink or swell in thepresence of water or oil in the fluid. Thus, a chemical sensor asdisclosed herein may be used to measure water and oil content in awater/oil mixture.

In some embodiments, sensitized coatings 212, 222, 232, and 242 targetgaseous hydrocarbons ranging from methane to hexane, and otherhydrocarbons and related chemical species of relevance to the oil andgas industry. In such embodiments, sensitized coatings 212, 222, 232,and 242 may include a thin polymer layer related to the selectedhydrocarbon. Moreover, in some embodiments coatings 212, 222, 232, and242 may include embedded nanoparticles to enhance target specificity,such as metal nanoclusters, quantum dots, and plasmon resonant schemes.Other embodiments include coatings 212, 222, 232, and 242 having ionsensitivity for applications such as pH sensors.

Analytes or characteristics that may be of relevance for targeting withsensors as disclosed herein include Iron ions or Alkaline metalsdissolved in fluid 150. In some embodiments, it is desirable to measuregaseous concentrations in fluid 150, such as CO₂ or Methane (CH₄). Moregenerally, sensors consistent with embodiments disclosed herein mayinclude pollutants, agrochemicals, nerve agents, explosives,pharmaceuticals, and controlled substances (e.g., illegal drugs).

Accordingly, sensors as disclosed herein may have multiple applicationsdepending on the target analyte in fluid 150. For example, applicationsfor measuring bacteria contamination in fluid 150 include specificbacterial antibodies in sensitized coatings 212, 222, 232, and 242.Moreover, in some embodiments a sensor as disclosed herein includes atleast one of coatings 212, 222, 232, and 242 sensitized with an antibodyhaving affinity to certain types of cancer cells, or to acarcinoembryonic antigen (CEA). More generally, sensitized coatings 212,222, 232, and 242 may target pathogens associated with a disease such asa bacterium, a unicellular microorganism, a strand of nucleic acid(e.g., DNA or RNA), a protein or a peptide. Other examples of targetpathogens for sensitized coatings 212, 222, 232, and 242 include, butare not limited to, Bacillus anthracis (Anthrax), Mycobacteriumtuberculosis lipoarabinomannan (LAM), Vibrio cholerae, Escherichia Coli(E. Coli), or the Influenza virus. Other biological agents targeted bysensitized coatings 212, 222, 232, and 242 include spores, toxins,viruses, and water borne pathogens. Accordingly, coatings 212, 222, 232,and 242 may include covalently bonding an antibody or antigen on theexposed surface of waveguides 214. Thus, sensors as disclosed herein areconfigured to determine a unicellular microorganism presence in asample, or a unicellular microorganism concentration in the sample.

Other examples for the use of sensors as disclosed herein include DNAsensors having short, single-stranded (desoxyribonucleicacid) DNAoligonucleotides grown on the surface of a quartz or silica waveguide214. Sensitized coatings 212, 222, 232, and 242 for use in biologicalsensing may include material layers such as silane-based self-assembledmonolayers. Accordingly, silane-based monolayers may be sensitized byamine radical termination including a mixture of carboxylicacid-terminated polyethylene glycol (PEG) chains.

In fluid 150, sensitized coatings 212, 222, 232, and 242 may reachequilibrium with a target analyte concentration after a given responsetime. It is desirable that the equilibrium be reached below a saturationpoint for a plurality of ligands included in sensitized coatings 212,222, 232, and 242. In that regard, when target analyte concentrationincreases, it may be desirable that the coating response increases at afirst rate. When target analyte concentration decreases, it is desirablethat the coating response decreases at an equivalent second rate.Accordingly, it is desirable that sensitized coatings 212, 222, 232, and242 have a reversible and linear response to target analyteconcentration. Thus, it is desirable that sensitized coatings 212, 222,232, and 242 reach an equilibrium point that is proportional to analyteconcentration in fluid 150. Response times and saturation points varysubstantially from one type of sensitized coating to another. Ingeneral, it is desirable that sensitized coating 212, 222, 232, and 242have a fast, linear, and reversible response.

In order to correct for aging and degradation effects in sensitizedcoatings 212, 222, 232, and 242, some embodiments include periodiccalibration procedures on sensors 200 a and 200 b. Furthermore, someembodiments include a heater to drive back the sensitized coating to abaseline (or unsaturated) value. Some embodiments include calibrationmeasurements to determine sensor replacement or when to refresh or cleanthe sensitized coating.

FIG. 3A illustrates a cross-sectional view of an exemplary sensor 300 aincorporating waveguides 214 in 3D substrate 205 a, according to someembodiments. Sensor 300 a is similar to sensor 200 a, described indetail above (cf. FIG. 2A). Sensor 300 a includes sensing channels 310,320, 330 and 340. Sensing channel 310 includes sensitized coating 212,and therefore has a similar function as sensing channel 210 in sensor200 a. Likewise, sensing channel 320 includes sensitized coating 222,and therefore has a similar function as sensing channel 220 in sensor200 a. Sensing channel 330 includes sensitized coating 232, andtherefore has a similar function as sensing channel 230 in sensor 100 a.Moreover, sensing channel 340 includes sensitized coating 242, andtherefore has a similar function as sensing channel 240 in sensor 200 a.

As illustrated, sensing channels 310 and 340 share a first referencewaveguide 214 r, and sensing channels 320 and 330 share a secondreference waveguide 214 r. Thus, sensor 300 a makes an efficient use ofthe total number of waveguides 214 embedded in 3D substrate 205 a.Accordingly, sensor 300 a increases the possible number of analytesdetected simultaneously by reducing the total number of referencewaveguides 214 r.

FIG. 3B illustrates a cross-sectional view of a chemical sensor 300 bincorporating waveguides 214 in hollow 3D substrate 205 b, according tosome embodiments. Sensing channels 310, 320, 330, and 340 in FIG. 3B areas described in detail above in reference to FIG. 3A. Substrate 205 b isas described in FIG. 2B above.

More generally, embodiments consistent with the present disclosure use asingle reference waveguide with multiple sample waveguides for detectionof multiple analytes of interest. Furthermore, multiple analytedetection may be performed simultaneously or overlapping in time.

FIG. 4 illustrates a chemical sensor 400 incorporating waveguides 214(shown as waveguides 214 r and 214 s) in an exterior surface of 3Dsubstrate 205 a, according to some embodiments. Sensor 400 includes 3Dsubstrate 205 a inserted into a housing 401 containing fluid 150 flowingpast sensor 400 from a fluid inlet 405 to a fluid outlet 407. Coherentlight illuminates an input side of 3D substrate 205 a and detectors 418and 438 positioned at an output side of 3D substrate 205 a read theindividual interferometers formed by signal channels 310 and 330. Whilenot limiting, some embodiments of sensor 400 include a 3D substrate 205a of about 1″ to 2″ in length.

A signal electromagnetic radiation 410 s is coupled or otherwiseconveyed into waveguide 214 s and interacts with sensitized coating 212.As a result, a sample output signal 412 s emerges from waveguide 214 s.A reference electromagnetic radiation 410 r is coupled or otherwiseconveyed into waveguide 214 r to form a reference output signal 412 r.Sample output signal 412 s optically interacts with reference outputsignal 412 r to form interference pattern 415. Detector 418 measures aproperty of interference pattern 415. The distance between detector 418and the end of waveguides 214 is selected to capture a specific portionof interference pattern 415. In some embodiments, detector 418 may beplaced in the near field (about a few wavelengths away from the end ofwaveguides 214), to have greater sensitivity to changes in interferencepattern 415. Further, in some embodiments, detector 418 may be placedwith a sensitive area overlapping a peak in interference pattern 415.Some embodiments may include detector 418 with a sensitive areaoverlapping a dark node of interference pattern 415. Moreover, in someembodiments a sensitive area of detector 418 may overlap a transitionregion in interference pattern 415, the transition region including aportion of a peak and a portion of a dark node. In yet otherembodiments, detector 418 may include a sensor array including a lineararray of optical fibers, each optical fiber connected to a remote photodetector. In such a configuration, waveguides 214 may also be remotelyilluminated and interrogated via fiber (e.g., from the surface indownhole applications); thus, sources and detectors can be locatedremotely, according to some embodiments. For downhole applications, thismeans at the surface, away from the harsh downhole environment that isnot amenable to light sources and detectors.

In a similar manner, a first electromagnetic radiation 430 s, and asecond electromagnetic radiation 430 r are coupled or otherwise conveyedinto waveguides 214 s and 214 r, respectively. A sample output signal432 s is the result of interaction between first electromagneticradiation 430 s and sensitized coating 232. Accordingly, sample outputsignal 432 s interacts with reference output signal 432 r to forminterference pattern 435. Detector 438 measures a property ofinterference pattern 435.

In one or more embodiments, electromagnetic radiation 410 s, 410 r, 430s, and 430 r is part of a collimated, coherent beam of lightilluminating the left hand side of the structure. Some embodiments mayinclude electromagnetic radiation 410 s coherent with electromagneticradiation 410 r as part of a focusing beam. Other configurations ofelectromagnetic radiation 410 s and electromagnetic radiation 410 r mayinclude non-collimated beams. Accordingly, interference patterns 415 and435 may be formed as sample output signal 412 s and reference outputsignal 412 r each propagate through free space.

In some embodiments, an optical element (not shown) may be placedbetween the output side of waveguides 214 and detector 418. For example,in some embodiments a micro-lens array may be placed between waveguides214 and detector 418 to more efficiently direct interference pattern 415to the sensitive area in detector 418. Detector 418 may be a singlereceiver to determine the brightness or irradiance of a centralinterference fringe in pattern 415 in configuration where the centralfringe is approximately Gaussian in shape. Accordingly, pattern 415moves up and down with respect to detector 418 in FIG. 4 in response tophase differences between sample output signal 412 s and referenceoutput signal 412 r exiting waveguides 214 s and 214 r, respectively.Alternately, detector 418 may include an array of sensors used to betterdetermine the position of the central fringe and secondary interferencesin pattern 415, which may be also be analyzed to determine the phasedifference. Detector 418 may include a lens to focus the central area ofinterference pattern 415 onto an optical fiber, or a plurality ofoptical fibers. Accordingly, light forming interference pattern 415 canbe transmitted to a remote photodiode sensor via the optical fiber, orthe plurality of optical fibers receiving at least a portion ofinterference pattern 415 at a selected location.

In embodiments consistent with the present disclosure, detectors 418 and438 may include a plurality of sensitive areas in a detector array.Thus, detectors 418 and 438 may collect a portion of interferencepatterns 415 and 435, respectively, and perform a detailed analysis orcomputation. In embodiments consistent with the present disclosure,detectors 418 and 438 may be included in a detector array. In someembodiments, the entire body of sensor 400 may be immersed in fluid 150to perform simultaneous or time overlapped measurements of multipleanalytes. In yet other embodiments, only a portion of the OD insubstrate 205 a may be exposed to the fluid (e.g., the portion exposingsensing channel 210) at a given moment. In such a configuration, sensor400 may incorporate a rotating mechanism to rotate substrate 205 a aboutits longitudinal axis to perform a second measurement (e.g., rotatingsubstrate 205 a to expose sensing channel 220). Accordingly, in someembodiments housing 401 maintains detectors 415 and 435 in a desiredposition relative to 3D substrate 205 a. In some embodiments, substrate205 a moves longitudinally inside housing 401 so that a fresh portion ofcoatings 212 and 232 is exposed to fluid 150.

FIG. 5 illustrates a sensor 500 incorporating waveguides 214 in aninterior surface of a 3D substrate 205 b, according to some embodiments.In FIG. 5, fluid 150 flows from an inlet 505 to outlet 507 through aportion within an inner diameter of substrate 205 b. FIG. 5 depicts onesensing channel 210 for illustration purposes only. A plurality ofsensing channels may be included, consistent with embodiments disclosedherein (e.g., channels 210, 220, 230, 240, cf. FIG. 2B, or channels 310,320, 330, and 340, cf. FIG. 3B).

FIGS. 4 and 5 illustrate a Mach-Zehnder configuration where a beamsplitter is replaced by illuminating waveguides 214 s and 214 r withcoherent, collimated light. Another advantageous feature in someembodiments of chemical sensors 400 and 500 is that output light 412 sand 412 r is combined in free space propagation into interferencepattern 415 as in a “two slit” interference pattern. Accordingly,embodiments of chemical sensors consistent with FIGS. 4 and 5 arecompact, simpler and cheaper to fabricate than existing interferometricwaveguide based chemical sensors.

FIG. 6A illustrates a cross-sectional view of a chemical sensor 600 aincorporating waveguides 214 in an exterior surface of a 3D substrate205 a, according to some embodiments. A mask 605 a in sensor 600 aoverlaps transparent portions that are not waveguides 214 on the side ofsensor 600 a including the optical output of waveguides 214. Mask 605 aimproves the signal-to-noise ratio (SNR) from the output of waveguides214.

FIG. 6B illustrates a cross-sectional view of a chemical sensor 600 bincorporating waveguides 214 in an interior surface of a 3D substrate,according to some embodiments. A mask 605 b (best seen in FIG. 6C)included in sensor 600 b overlaps the end of the sensor tube, serving asimilar purpose as mask 605 a in sensor 600 a, above (cf. FIG. 6A).

Masks 605 a and 605 b block background electromagnetic radiation thatmay propagate through the bulk of 3D substrates 205 a and 205 b and mayconfuse the interference pattern formed at the detectors (e.g.,interference patterns 415 and 435, cf. FIG. 4). In that regard, masks605 a and 605 b may be formed of a material that is opaque orsubstantially opaque to the electromagnetic radiation propagatingthrough waveguides 214. Masks 605 a and 605 b limit the illuminationfrom light source 102 mostly to waveguides 214. Accordingly, masks 605 aand 605 b avoid illumination of the entire 3D structure, which is glassin some embodiments. In some embodiments, the portion of the crosssection of the 3D structure occupied by waveguides 214 is small incomparison to the entire cross section of the 3D structure. Accordingly,masks 605 a and 605 b increase the optical interferometric signal over abackground optical signal, thus facilitating phase difference detectionbetween waveguides 214 r and 214 s.

FIG. 6C illustrates a side view of sensor 600 a of FIG. 6A and sensor600 b of FIG. 6B, according to some embodiments. As shown in FIG. 6C,mask 605 a is disposed on a surface of substrate 205 a facing detectors418 and 438 (cf. FIG. 4). Likewise, mask 605 b is disposed on a surfaceof substrate 205 b facing detector 418 (cf. FIG. 5).

FIG. 7 illustrates a flow chart including steps in a method 700 forfabricating a sensor incorporating waveguides in a 3D substrate,according to some embodiments. The sensor in method 700 may include a 3Dsubstrate having a cross-section and a length, the substrate supportinga plurality of waveguides embedded in the substrate (e.g., waveguides214 in sensors 100 a, 100 b, 300 a, and 300 b, cf. FIGS. 2A, 2B, 3A, and3B, respectively). The substrate may further include an exposed surfacehaving at least a portion of a side surface of each waveguide, andsensitized coatings in the portion of the side surface of at least oneof the plurality of waveguides (e.g., sensitized coatings 212, 222, 232,and 242). Methods consistent with the present disclosure may include atleast one of the steps in method 700, and not others. Likewise, methodsconsistent with method 700 may include all the steps in method 700, inaddition to other steps. Moreover, the specific order of the stepsillustrated in FIG. 7 is not limiting of different embodimentsconsistent with method 700. In that regard, methods consistent withmethod 700 may include steps as illustrated in FIG. 7 performed indifferent order, or at least two or more steps overlapping in time, oreven two or more steps performed simultaneously.

Step 702 includes forming the 3D substrate in a shape that fits into afluid container, such that the 3D substrate may have at least onesurface exposed to the fluid. Accordingly, in some embodiments step 702may include using a preform in the shape of a solid or hollow rodstructure. Step 702 may also include selecting a material having a givenindex of refraction for the preform (e.g., n₂). Step 702 should alsoinclude forming longitudinal regions with a higher refractive index thanthe bulk regions. The regions with higher refractive index will form thewaveguides, after drawing the preform down to its final size. Forexample, step 702 may include selecting a 3D structure made of glass.Step 704 includes forming at least two channels on an exposed surface ofthe 3D substrate. The at least two channels in step 704 will becomewaveguides once the preform is formed into a waveguide structure, whenthe preform is drawn to its final size. Accordingly, step 704 mayinclude selectively increasing the index of refraction of the selectedportions of the preform (i.e., the at least two channels) to a value n₁(n₂<n₁). In some embodiments, step 706 includes doping portions of theglass preform with heavy ions, or illuminating portions of the glasspreform with electromagnetic radiation (such as ultra-violet radiation,or X-ray radiation). A preform as used in steps 702 through 704 may beon the order of ½ to 3 inches in diameter, according to someembodiments. Step 704 may include depositing, growing, fusing,inserting, or otherwise embedding channels with higher refractive indexthan the majority of the preform, in the preform. Step 706 includesheating and drawing the 3D substrate to reduce an outer diameter (OD) ofthe waveguide structure. Furthermore, step 706 may include heating andpulling the modified preform to a desired length in a draw tower.

Step 708 includes applying a sensitive coating on an exposed side of oneof the waveguides. Accordingly, step 708 may include depositing achemically sensitive coating using a chemical vapor deposition (CVD)technique. Other techniques for thin layer deposition as used in thesemi-conductor and biomedical industries may be included and otherwiseemployed in step 708. Step 710 includes disposing a mask on surfaces ofthe 3D substrate. Accordingly, in some embodiments step 710 includesdisposing the mask on a surface that will face the detector.Furthermore, in some embodiments step 710 includes disposing a mask alsoin a surface of the 3D substrate facing the source of collimated light.In that regard, step 710 enhances removal of an optical background froma signal measured by the detector.

Step 712 includes disposing a detector at a selected position relativeto an optical output of each of the at least two waveguides.Accordingly, step 712 may include disposing the detector so that thesensitive area of the detector overlaps a peak, or a dark node in aninterference pattern formed by the waveguides embedded in the 3Dsubstrate. Moreover, step 712 may include disposing the detector so thatthe sensitive area of the detector overlaps a portion of a peak and aportion of a dark node in the interference pattern. Step 712 may furtherinclude disposing the 3D substrate including the waveguides, and thedetector, in a housing that protects the chemically sensitive coatingand maintains the detector in the desired position.

FIG. 8 illustrates a flow chart including steps in a method 800 formeasuring a characteristic of a sample using a sensor, according to someembodiments. Method 800 may include using a light source, abeam-splitter, a sensor, and a detector in an interferometerconfiguration (e.g., light source 102, beam-splitter 104, sensor 100,and detector 118, cf. FIG. 1). Alternatively, the input beam splittermay be omitted by illuminating both waveguides of a sensinginterferometer by a single, collimated, coherent beam that overlaps thetwo waveguides. The sensor may include a substrate having across-section and a length, the substrate supporting a plurality ofwaveguides embedded in the substrate (e.g., substrates 205 a and 205 b,and waveguides 214, cf. FIGS. 4 and 5). An exposed surface of thesubstrate includes least a portion of a side surface of each of theplurality of waveguides. The plurality of waveguides includes at least asensing channel having a sample waveguide and a reference waveguide(e.g., sensing channels 210, 220, 230, and 240, cf. FIGS. 2A, B).Accordingly, the sample waveguide may include a sensitized coating in aside surface that is included in the exposed surface of the substrate(e.g., sensitized coatings 212, 222, 232, and 242, cf. FIGS. 2A, B).Moreover, method 800 may be performed by an analyzer including aprocessor circuit executing commands stored in a memory circuit (e.g.,analyzer 160, processor circuit 161, and memory circuit 162).

Methods consistent with the present disclosure may include at least oneof the steps in method 800, and not others. Likewise, methods consistentwith method 800 may include all the steps in method 800, in addition toother steps. Moreover, the specific order of the steps illustrated inFIG. 8 is not limiting of different embodiments consistent with method800. In that regard, methods consistent with method 800 may includesteps as illustrated in FIG. 8 performed in different order, or at leasttwo or more steps overlapping in time, or even two or more stepsperformed simultaneously.

Step 802 includes exposing a sensitive surface of the sensor to a fluid.In some embodiments, step 802 includes allowing a target analyte toreach equilibrium on the sensitive surface of the sensor. Step 804includes directing a first portion of light through a first waveguide inthe sensor. In some embodiments, step 804 may further include splittinga coherent light beam using a beam splitter element and selecting thefirst portion of light from a first port in the beam splitter. Step 806includes directing a second portion of light through a second waveguidein the sensor. Accordingly, step 806 may include selecting the secondportion of light from a second port in the beam splitter. In someembodiments, steps 804 and 806 take place simultaneously.

Step 808 includes obtaining a phase relation between the first portionof light and the second portion of light at the output of the first andsecond waveguides. Accordingly, step 808 may include placing a phaseretardation element in the optical path length of the first portion oflight or the second portion of light between the light source and atleast one of the first and second waveguides. In some embodiments, step808 may include selecting a light beam having a coherence length longerthan a length of the waveguides in the sensor. In some embodiments, step808 includes splitting a light beam from a light source into the firstportion of light and the second portion of light with a phase-preservingbeam splitter element. Accordingly, step 808 includes obtaining a phasedifference that results from the different phase velocities (i.e.optical path lengths) between a sensitized waveguide and a referencewaveguide, as disclosed herein.

Step 810 includes detecting an interference signal with the detector. Insome embodiments, step 810 includes detecting a portion of theinterference signal comprising at least one of a peak, a dark node, or aportion of a peak and a dark node. In some embodiments, step 810 mayinclude determining an interference pattern using an array of sensitiveareas in the detector, or an array of detectors. Accordingly, step 810may include detecting an interference pattern with a two-dimensionaldetector array. Furthermore, in some embodiments step 810 includesdetecting an interference pattern with a one-dimensional detector array.And step 812 includes determining the characteristic of the sample basedon a change in the interference signal from the detector. In someembodiments, step 812 includes determining an analyte concentrationbased on a change in the interference signal from the detector.Accordingly, step 812 may include finding the characteristic of thesample in a lookup table having a list of characteristics of the sampleand a list of changes in interference signal values.

FIG. 9 illustrates an exemplary drilling system 900 employing a sensor901 incorporating waveguides in a 3D substrate, according to someembodiments. Sensor 901 may be the same as or similar to any one ofsensors 100, 200 a, 200 b described in detail in FIG. 1 and in FIGS.2A-2B above. Boreholes may be created by drilling into the earth 902using drilling system 900. Drilling system 900 may be configured todrive a bottom hole assembly (BHA) 904 positioned or otherwise arrangedat the bottom of a drill string 906 extended into the earth 902 from aderrick 908 arranged at the surface 910. The derrick 908 includes akelly 912 used to lower and raise the drill string 906.

The BHA 904 may include a drill bit 914 operatively coupled to a toolstring 916 which may be moved axially within a drilled wellbore 918 asattached to the drill string 906. During operation, drill bit 914penetrates the earth 902 to form wellbore 918. BHA 904 providesdirectional control of drill bit 914 as it advances into the earth 902.Tool string 916 can be semi-permanently mounted with various measurementtools such as a measurement-while-drilling (MWD) tool and alogging-while-drilling (LWD) tool, and sensor 901 may form part of oneof the MWD or LWD tools to obtain downhole measurements of drillingconditions. In other embodiments, the measurement tools may beself-contained within the tool string 916, as shown in FIG. 9. In someembodiments, tool string 916 may include a fiber optic cable coupling alight source at surface 910 to sensor 901 (e.g., light source 102, cf.FIG. 1). The fiber optic cable may be configured to conveyelectromagnetic radiation to sensor 901 (e.g., electromagnetic radiation110 s and electromagnetic radiation 110 r, cf. FIG. 1).

Fluid or “mud” from a mud tank 920 may be pumped downhole using a mudpump 922 powered by an adjacent power source, such as a prime mover ormotor 924. The mud may be pumped from the mud tank 920, through a standpipe 926, which feeds the mud into the drill string 106 and conveys thesame to the drill bit 914. The mud exits one or more nozzles arranged inthe drill bit 914 and in the process cools the drill bit 914. Afterexiting the drill bit 914, the mud circulates back to the surface 910via the annulus defined between the wellbore 918 and the drill string906, and in the process returns drill cuttings and debris to thesurface. The cuttings and mud mixture are passed through a flow line 928and are processed such that a cleaned mud is returned down hole throughthe stand pipe 926 once again. Sensor 901 may be configured to measurecharacteristics of the mud near where drill bit 914 forms wellbore 918.In that regard, mud in the wellbore near drill bit 914 may be the fluidto which sensor 901 is exposed, for measurement (e.g., fluid 150, cf.FIGS. 1, 4 and 5). In that regard, measurement procedures using sensor901 may include any one or all of the steps in a method for measuring acharacteristic of a sample using a sensor as disclosed herein (e.g.,method 800, cf. FIG. 8).

Although drilling system 900 is shown and described with respect to arotary drill system in FIG. 9, those skilled in the art will readilyappreciate that many types of drilling systems can be employed incarrying out embodiments of the disclosure. For instance, drills anddrill rigs used in embodiments of the disclosure may be used onshore (asdepicted in FIG. 9) or offshore (not shown). Offshore oil rigs that maybe used in accordance with embodiments of the disclosure include, forexample, floaters, fixed platforms, gravity-based structures, drillships, semi-submersible platforms, jack-up drilling rigs, tension-legplatforms, and the like. It will be appreciated that embodiments of thedisclosure can be applied to rigs ranging anywhere from small in sizeand portable, to bulky and permanent. Further, although described hereinwith respect to oil drilling, various embodiments of the disclosure maybe used in many other applications. For example, disclosed methods canbe used in drilling for mineral exploration, environmentalinvestigation, natural gas extraction, underground installation, miningoperations, water wells, geothermal wells, and the like. Further,embodiments of the disclosure may be used in weight-on-packersassemblies, in running liner hangers, in running completion strings,etc., without departing from the scope of the disclosure.

FIG. 10 illustrates a well system 1000 employing a sensor 1001incorporating waveguides in a 3D substrate, according to someembodiments. Sensor 1001 may be the same as or similar to any one ofsensors 100, 200 a, 200 b described in detail in FIG. 1 and in FIGS.2A-B above. As illustrated, well system 1000 may include a service rig1020 that is positioned on the earth's surface 1040 and extends over andaround a wellbore 1060 that penetrates a subterranean formation 1080.Service rig 1020 may be a drilling rig, a completion rig, a workoverrig, or the like. In some embodiments, service rig 1020 may be omittedand replaced with a standard surface wellhead completion orinstallation. Moreover, while well system 1000 is depicted as aland-based operation, it will be appreciated that the principles of thepresent disclosure could equally be applied in any sea-based or sub-seaapplication where service rig 1020 may be a floating platform orsub-surface wellhead installation, as generally known in the art.

Wellbore 1060 may be drilled into subterranean formation 1080 using anysuitable drilling technique and may extend in a substantially verticaldirection away from the earth's surface 1040 over a vertical wellboreportion 1100. At some point in wellbore 1060, vertical wellbore portion1100 may deviate from vertical relative to the earth's surface 1040 andtransition into a substantially horizontal wellbore portion 1120. Insome embodiments, wellbore 1060 may be completed by cementing a casingstring 1140 within wellbore 1060 along all or a portion thereof. As usedherein, “casing string” may refer to any downhole tubular or string oftubulars known to those skilled in the art including, but not limitedto, wellbore liner, production tubing, drill string, and other downholepiping systems.

System 1000 may further include a downhole tool 1160 conveyed intowellbore 1060. Downhole tool 1160 may be coupled or otherwise attachedto a conveyance 1180 that extends from service rig 1020. Conveyance 1180may be, but is not limited to, a wireline, a slickline, an electricline, coiled tubing, or the like. In some embodiments, device 1160 maybe pumped downhole to a target location within wellbore 1060 usinghydraulic pressure applied from service rig 1020 at surface 1040. Insome embodiments, downhole tool 1160 may be conveyed to the targetlocation using gravitational or otherwise natural forces. Downhole tool1160 can be semi-permanently mounted with various measurement devicessuch as sensor 1001. In some embodiments, conveyance 1180 may include afiber optic cable coupling a light source at surface 1040 to sensor 1001(e.g., light source 102, cf. FIG. 1). The fiber optic cable may beconfigured to convey electromagnetic radiation to sensor 1001 (e.g.,electromagnetic radiation 110 s and electromagnetic radiation 110 r, cf.FIG. 1).

Even though FIG. 10 depicts downhole tool 1160 as being arranged andoperating in horizontal portion 1120, embodiments disclosed herein areequally applicable for use in portions of wellbore 1060 that arevertical, deviated, or otherwise slanted. Moreover, use of directionalterms such as above, below, upper, lower, upward, downward, uphole,downhole, and the like are used in relation to the illustrativeembodiments as they are depicted in the figures, the upward directionbeing toward the top of the corresponding figure and the downwarddirection being toward the bottom of the corresponding figure, theuphole direction being toward the surface of the well and the downholedirection being toward the toe of the well.

Those skilled in the art will readily appreciate that the methodsdescribed herein, or large portions thereof, may be automated at somepoint such that a computerized system may be programmed to design,predict, and devices that are more robust for compact optical systemsoperating in extreme environments. Computer hardware used to implementthe various methods and algorithms described herein can include aprocessor configured to execute one or more sequences of instructions,programming stances, or code stored on a non-transitory,computer-readable medium. The processor can be, for example, a generalpurpose microprocessor, a microcontroller, a digital signal processor,an application specific integrated circuit, a field programmable gatearray, a programmable logic device, a controller, a state machine, agated logic, discrete hardware components, an artificial neural network,or any like suitable entity that can perform calculations or othermanipulations of data. In some embodiments, computer hardware canfurther include elements such as, for example, a memory (e.g., randomaccess memory (RAM), flash memory, read only memory (ROM), programmableread only memory (PROM), electrically erasable programmable read onlymemory (EEPROM)), registers, hard disks, removable disks, CD-ROMS, DVDs,or any other like suitable storage device or medium.

Executable sequences described herein can be implemented with one ormore sequences of code contained in a memory. In some embodiments, suchcode can be read into the memory from another machine-readable medium.Execution of the sequences of instructions contained in the memory cancause a processor to perform the process steps described herein. One ormore processors in a multi-processing arrangement can also be employedto execute instruction sequences in the memory. In addition, hard-wiredcircuitry can be used in place of or in combination with softwareinstructions to implement various embodiments described herein. Thus,the present embodiments are not limited to any specific combination ofhardware and/or software.

As used herein, a machine-readable medium will refer to any medium thatdirectly or indirectly provides instructions to a processor forexecution. A machine-readable medium can take on many forms including,for example, non-volatile media, volatile media, and transmission media.Non-volatile media can include, for example, optical and magnetic disks.Volatile media can include, for example, dynamic memory. Transmissionmedia can include, for example, coaxial cables, wire, fiber optics, andwires that form a bus. Common forms of machine-readable media caninclude, for example, floppy disks, flexible disks, hard disks, magnetictapes, other like magnetic media, CD-ROMs, DVDs, other like opticalmedia, punch cards, paper tapes and like physical media with patternedholes, RAM, ROM, PROM, EPROM and flash EPROM.

Embodiments disclosed herein include:

A. A sensor for measuring a characteristic of a substance that includesa substrate having a cross-section and a length, a plurality ofwaveguides embedded in the substrate, the substrate providing an exposedsurface, the exposed surface comprising a portion of a side surface ofat least one of the plurality of waveguides, and a sensitized coatingpositioned on the exposed surface of the at least one of the pluralityof waveguides.

B. A method for fabricating a sensor that includes forming a substratein a three-dimensional shape, arranging at least two waveguides on anexposed surface of the substrate, applying a sensitive coating on anexposed side of one of the at least two waveguides, the exposed sidebeing adjacent the exposed surface, and disposing a detector at aselected position relative to an optical output of each of the at leasttwo waveguides.

C. A method for measuring a characteristic of a substance that includesexposing a surface of a sensor to the substance, the sensor including asubstrate, a plurality of waveguides embedded in the substrate, and asensitized coating positioned on a portion of at least one of theplurality of waveguides, directing a first portion of light through afirst waveguide of the plurality of waveguides and thereby generating afirst output signal, directing a second portion of light through asecond waveguide of the plurality of waveguides and thereby generating asecond output signal, obtaining a phase relation between the firstportion of light and the second portion of light at an output of thefirst and second waveguides, generating an interference signal bycombining the first and second output signals, detecting at least aportion of the interference signal with a detector, and determining thecharacteristic of the substance based on a change in a feature of theinterference signal detected with the detector.

Each of embodiments A, B, and C may have one or more of the followingadditional elements in any combination: Element 1: wherein the exposedsurface is curved in a direction perpendicular to a light propagation inthe waveguide. Element 2: further comprising a detector arranged toreceive an interference pattern generated from two waveguides of theplurality of waveguides, and configured to generate a signalcorresponding to a change in an interference pattern, the change in theinterference pattern induced by the characteristic of the substance.Element 3: wherein the interference pattern is formed in a free spacebetween the detector an optical output of the waveguides. Element 4:wherein the sensitized coating comprises one of a chemically sensitivelayer, a biologically sensitive layer, a hydrophilic layer, or ahydrophobic layer. Element 5: wherein the plurality of waveguidescomprise a sample waveguide having the sensitized coating positionedthereon and being optically coupled with a signal electromagneticradiation portion, a reference waveguide adjacent the sample waveguideand being optically coupled with a reference electromagnetic radiationportion, the reference radiation having a determined phase relation withthe sample radiation. Element 6: further comprising a second samplewaveguide being optically coupled with a second signal electromagneticradiation portion, wherein the second signal electromagnetic radiationportion has a determined phase relation with the referenceelectromagnetic radiation portion. Element 7: further comprising a maskapplied to the substrate to prevent background radiation in thesubstrate from reaching a detector. Element 8: wherein the sensitizedcoating targets one of the group consisting of water, gas, oil, methane,a hydrocarbon, a unicellular microorganism, an iron ion, and an alkalimetal. Element 9: wherein the plurality of waveguides include at least asample waveguide and a reference waveguide, the sensor furthercomprising a detector array to measure at least a portion of aninterference pattern generated by the sample waveguide and the referencewaveguide. Element 10: wherein the sensitized coating is configured tocontact a substance including a target analyte. Element 11: wherein thesubstrate is cylindrical and the exposed surface is positioned at aninner diameter of the substrate.

Element 12: further comprising disposing a mask on a surface of thesubstrate that faces the detector. Element 13: further comprisingheating and drawing the substrate to reduce an outer diameter (OD) ofthe waveguide structure. Element 14: wherein the at least two waveguidesinclude a sample waveguide and a reference waveguide, the method furthercomprising determining an interference pattern for light emerging fromthe sample waveguide and the reference waveguide to select a positionfor disposing the detector. Element 15: further comprising overlapping asensitive area of the detector with at least one of a peak of theinterference pattern, a dark node of the interference pattern, and aportion of a peak and a dark node of the interference pattern.

Element 16: wherein exposing the sensitive surface of the sensorcomprises allowing a target analyte to reach equilibrium on thesensitive surface of the sensor. Element 17: wherein obtaining a phaserelation between the first portion of light and the second portion oflight comprises splitting a light beam from a light source into thefirst portion of light and the second portion of light with aphase-preserving beam splitter element. Element 18: wherein detectingthe interference signal with the detector comprises detecting a portionof the interference signal comprising at least one of a peak, a darknode, or a portion of a peak and a dark node. Element 19: whereindetecting the interference signal with the detector comprises couplingat least a portion of the interference signal to an optical fiber andtransmitting the coupled portion to a remotely located detector. Element20: wherein obtaining a phase relation between the first portion oflight and the second portion of light comprises illuminating the firstand second waveguides with a collimated and coherent light. Element 21:wherein determining the characteristic of the substance comprisesfinding the characteristic of the substance in a lookup table having alist of characteristics of the substance and a list of changes ininterference signal values. Element 22: wherein determining thecharacteristic of the substance comprises determining at least one of awater concentration, a gas concentration, an oil concentration, awater-to-oil ratio, a methane concentration, or a hydrocarbonconcentration, a unicellular microorganism presence or a unicellularmicroorganism concentration.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered,combined, or modified and all such variations are considered within thescope and spirit of the present invention. The invention illustrativelydisclosed herein suitably may be practiced in the absence of any elementthat is not specifically disclosed herein and/or any optional elementdisclosed herein. While compositions and methods are described in termsof “comprising,” “containing,” or “including” various components orsteps, the compositions and methods can also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is:
 1. A method of fabricating a sensor, the methodcomprising: arranging at least two waveguides on an exposed surface of athree-dimensional substrate; applying a sensitive coating on an exposedside of one of the at least two waveguides along a longitudinal axis ofthe sensor, the exposed side being adjacent to the exposed surface; anddisposing a mask on a surface of the three-dimensional substrate that isorthogonal to the longitudinal axis of the sensor, the mask being incontact with transparent portions of the three-dimensional substrate andthe at least two waveguides.
 2. The method of claim 1, furthercomprising: heating and drawing the three-dimensional substrate toreduce an outer diameter (OD) of the at least two waveguides.
 3. Themethod of claim 1, further comprising: disposing a detector at aselected position relative to an optical output of each of the at leasttwo waveguides.
 4. The method of claim 3, wherein the at least twowaveguides include a sample waveguide and a reference waveguide, themethod further comprising determining an interference pattern for lightemerging from the sample waveguide and the reference waveguide to selecta position for disposing the detector.
 5. The method of claim 4, furthercomprising: overlapping a sensitive area of the detector with at leastone of a peak of the interference pattern, a dark node of theinterference pattern, and a portion of a peak and a dark node of theinterference pattern.
 6. The method of claim 1, wherein the exposedsurface is curved in a direction perpendicular to a light propagation inthe at least two waveguides.
 7. The method of claim 1, wherein thesensitized coating comprises one of a chemically sensitive layer, abiologically sensitive layer, a hydrophilic layer, or a hydrophobiclayer.
 8. The method of claim 1, wherein the arranging the at least twowaveguides comprises: arranging a sample waveguide having the sensitizedcoating for optically coupling with a signal electromagnetic radiation;and arranging a reference waveguide adjacent to the sample waveguide foroptically coupling with a reference electromagnetic radiation, thereference electromagnetic radiation having a determined phase relationwith the signal electromagnetic radiation.
 9. A method of fabricating asensor for measuring a characteristic of a substance, comprising:arranging a plurality of sensing channels along an exposed surface of asubstrate, each of the plurality of sensing channels comprising aplurality of waveguides embedded in the substrate, wherein a first groupof sensing channels of the plurality of sensing channels share a firstreference waveguide of the plurality of waveguides and a second group ofsensing channels of the plurality of sensing channels share a secondreference waveguide of the plurality of waveguides, the first referencewaveguide being different from the second reference waveguide, theexposed surface comprising a portion of a side surface of at least oneof the plurality of waveguides; applying a sensitized coating on theexposed surface of the at least one of the plurality of waveguides alonga longitudinal axis of the sensor; and disposing a mask on a surface ofthe substrate that is orthogonal to the longitudinal axis of the sensor,the mask being in contact with transparent portions of the substrate andthe plurality of waveguides.
 10. The method of claim 9, wherein theexposed surface is curved in a direction perpendicular to a lightpropagation in the waveguide.
 11. The method of claim 9, furthercomprising: arranging a detector to receive an interference patterngenerated from two waveguides of the plurality of waveguides, thedetector being configured to generate a signal corresponding to a changein an interference pattern, the change in the interference patterninduced by the characteristic of the substance.
 12. The method of claim11, wherein the interference pattern is formed in a free space betweenthe detector and an optical output of the plurality of waveguides. 13.The method of claim 9, wherein the sensitized coating comprises one of achemically sensitive layer, a biologically sensitive layer, ahydrophilic layer, or a hydrophobic layer.
 14. The method of claim 9,wherein the arranging the plurality of sensing channels comprises:arranging a sample waveguide having the sensitized coating for opticallycoupling with a signal electromagnetic radiation; and arranging areference waveguide adjacent to the sample waveguide for opticallycoupling with a reference electromagnetic radiation, wherein thereference electromagnetic radiation has a determined phase relation withthe signal electromagnetic radiation.
 15. The method of claim 14,further comprising: arranging a second sample waveguide for opticallycoupling with a second signal electromagnetic radiation, wherein thesecond signal electromagnetic radiation has a determined phase relationwith the reference electromagnetic radiation.
 16. The method of claim 9,wherein the mask is disposed on the substrate to prevent backgroundradiation in the substrate from reaching a detector.
 17. The method ofclaim 9, wherein the sensitized coating targets one of a groupconsisting of water, gas, oil, methane, a hydrocarbon, a unicellularmicroorganism, an iron ion, and an alkali metal.
 18. The method of claim9, wherein the arranging the plurality of sensing channels comprises:arranging at least a sample waveguide and a reference waveguide, whereinthe method further comprises: arranging a detector array to measure atleast a portion of an interference pattern generated by the samplewaveguide and the reference waveguide.
 19. The method of claim 9,wherein the sensitized coating is configured to contact a substanceincluding a target analyte.
 20. The method of claim 9, wherein thesubstrate is cylindrical and the exposed surface is positioned at aninner diameter of the substrate.